1. Field of the Invention
The present invention pertains to a hydrorefining catalyst and a hydrorefining method using the catalyst, as well as a method of producing the catalyst, and in particular, to hydrorefining for removal of the metal content, such as nickel, vanadium, etc., contained in heavy oil.
2. Description of the Related Art
In general, it is necessary to pre-remove the metal content, such as vanadium, nickel, etc., that poisons desulfurizing and denitrifying active sites when performing hydrorefining, such as desulfurization and denitrification, etc., of heavy oil. In particular, when heavy oil having a high metal content, such as residue, etc is hydrorefined, much of the metal content accumulates in the peripheral part surface of the catalyst pellet, plugging the pores thereof there. Therefore, oil and hydrogen are prevented from diffusing to inside the catalyst pellet and the catalyst loses its activity. As a result, the catalyst must be replaced.
There is a demand for development of a long-life catalyst with which the metal content of the above-mentioned feed heavy oil is removed and there is long-term retention of high activity in order to continuously hydrorefine heavy oil with a high metal content, such as residue from atmospheric distillation and residue from vacuum distillation, etc., efficiently and with stability. Therefore, life is prolonged by, for instance, making pore diameter of the catalyst carrier uniform and large so that molecules comprising the metal content of the feed heavy oil are diffused to inside the catalyst and the active sites inside the catalyst are efficiently used. Moreover, a bimodal carrier having pores of 1,000 xc3x85 or larger called macropores as well as mesopores is being used as a catalyst carrier in order-to facilitate diffusion to the inside.
Furthermore, adjustment of the type, concentration, and combination of supported metals is also being used as .another method of prolonging catalyst life. In addition, methods are also being studied whereby the plugging that is caused by accumulation of metal content is prevented by using a combination of several types of catalysts with different pore distributions, supported metals, etc. However, even these methods cannot thoroughly satisfy the above-mentioned demand.
Japanese Patent Application Laid-Open No. 58-153539 discloses a hydrodesulfurization catalyst, characterized in that it is made from a porous aluminum carrier and molybdenum and phosphorus, and further, cobalt and/or nickel, to which at least one selected from the group consisting of potassium, rubidium, and cesium has further been added, supported on this carrier. This publication explains that activity is markedly improved simply by adding a trace of potassium, rubidium, or cesium to the catalyst system, but there is no description of the concentration distribution of the potassium in the catalyst.
Japanese Patent Application Laid-Open No. 61-283351 discloses a catalyst where the concentration of the hydrogenation active metal elements in the central part of the catalyst pellet is higher than the concentration in the peripheral part. It explains that as a result, accumulation of metal in the peripheral part of the catalyst pellet is prevented and life is prolonged. However, there is no description of a means other than the higher concentration of the hydrogenation active metal elements in the central part of the catalyst pellet for preventing metal accumulation.
Japanese Patent Application Laid-Open No. 9-240094 discloses that alkali metal in a catalyst supporting mainly an alkali metal such as potassium, etc., is stabilized when a non-metal element, such as phosphorus, etc. is also present. It explains that when molybdenum, nickel, etc. are present, the alkali metal is mainly present in the peripheral part edges of the catalyst. However, there is no indication as to the concentration distribution of the molybdenum, nickel, etc., in the catalyst. Furthermore, although Example 13 of Japanese Patent Application Laid-Open No. 9-240094 discloses a method of producing a catalyst containing molybdenum and potassium, catalyst carrier is first sprayed with ammonium molybdate and is then sprayed with a solution containing phosphoric acid and potassium nitrate. A catalyst with the molybdenum concentration distribution specified by the present invention is not obtained, even if this production method disclosed in Japanese Patent Application Laid-Open No. 9-240094 is used.
The present invention solves the above-mentioned problems of conventional technique, its object being to present a hydrorefining catalyst with which the fine pores in the catalyst are rarely plugged by the metal content and which can retain high activity for a long period of time. In particular, the object of the present invention is to present a hydrorefining catalyst with which the fine pores on the outside surface of the catalyst are not plugged by the metal content of hetero compounds, even when hydrocarbon oil with an asphaltene content of 2 wt % or more is hydrorefined, making it possible for the hetero compound to efficiently diffuse to inside the catalyst, and as a result, long-term retention of a state of high activity can be accomplished, a method of producing the same catalyst, and a hydrorefining method using the same catalyst.
As a result of performing intensive studies in order to accomplish the above-mentioned object, the inventors achieved the present invention upon discovering that catalyst activity is improved and life is prolonged when a potassium component for reducing molecular weight of compound containing hetero elements (sulfur, vanadium, nickel, etc.) and at least one type of hydrogenation active metal element selected from elements of Group 6, Group 8, Group 9, and Group 10 of the Periodic Table, which have excellent ability in terms of hydrogenation of hetero element-containing compounds, are present at a specific distribution inside the catalyst pellets.
In accordance with the first aspect of the present invention, a hydrorefining catalyst is presented, comprising a carrier consisting of porous inorganic oxide, 0.1 to 25 wt % of at least one hydrogenation active metal element selected from Group 6, Group 8, Group 9, and Group 10 of the Periodic Table (0.1 to 25 wt % in total if two or more types of hydrogenation active metal elements are contained), and 0.1 to 3 wt % potassium, wherein the concentration distribution of the above-mentioned hydrogenation active metal element(s) is even higher in the central part than in the peripheral part of the catalyst and the concentration distribution of the above-mentioned potassium is even higher in the peripheral part than in the central part of the catalyst. By means of the catalyst of the present invention, in which the concentration of hydrogenation active metal element(s) is distributed higher in the central part than in the peripheral part of the catalyst, vanadium and nickel that have been hydrocracked from feed oil can be accumulated to fullest measure in the peripheral part, as well as in the central part, of the catalyst, as shown in the examples that follow. Therefore, it is possible to realize extremely high demetalizing activity of the catalyst and to retain this activity over a long period of time.
The catalyst of the present invention preferably has a distance from the outside surface to the center of the catalyst of 0.3 to 1.8 mm. Moreover, this catalyst preferably contains 2 to 15 wt % in total of hydrogenation active metal element(s) and 0.1 to 3 wt % potassium. Furthermore, it is preferred that the catalyst of the present invention contains phosphorus, and the phosphorus may be distributed more in the peripheral part than in the central part of the catalyst. In addition, it is preferred that the above-mentioned hydrogenation active metal element be molybdenum or tungsten.
In accordance with the second aspect of the present invention, a multi-bed catalytic reactor is presented, comprising at least first and second catalyst beds, wherein the first catalyst bed contains the catalyst of the present invention and the second catalyst bed contains demetalizing catalyst or desulfurizing catalyst.
In accordance with the third aspect of the present invention, a hydrorefining method is presented, wherein the hydrorefining catalyst of the present invention is brought into contact with hydrocarbon oil, particularly hydrocarbon oil with an asphaltene content of at least 2 wt %, in the presence of hydrogen. By means of this method, demetalization or desulfurization can be conducted more efficiently by further bringing hydrocarbon oil that has been contacted with the above-mentioned hydrorefining catalyst into contact with demetalizing or desulfurizing catalyst.
In accordance with the fourth aspect of the present invention, a method of producing a hydrorefining catalyst is presented, comprising the steps of impregnating porous inorganic oxide carrier with a phosphoric acid compound;
impregnating the porous inorganic oxide carrier with potassium compound; and impregnating the porous inorganic oxide carrier with at least one hydrogenation active metal element selected from elements of Group 6, Group 8, Group 9, and Group 10 of the Periodic Table, wherein the above-mentioned step of impregnation with the phosphoric acid compound is performed first or simultaneously with the other two steps, or it is performed simultaneously with one of the two steps and before the other step. For instance, the carrier is impregnated with the phosphoric acid compound and the above-mentioned hydrogenation active metal element together, and then the carrier is impregnated with the potassium compound.